Sensor arrangements, for example microphones, are used to record ambient noises or ambient sound. In order to provide a good quality of the recorded sound or in order to meet customer requirements, a high degree of linearity, high signal-to-noise ratios (SNR) or the correspondence with a predefined spectral mask may be necessary for the response function of a microphone.
As illustrated in the block diagram in FIG. 9, a conventional microphone 900 has a microphone diaphragm 902, for example a micro-electromechanical diaphragm (MEMS). The diaphragm 902 is deflected from a rest position by means of sound-induced pressure fluctuations and in the process generates an analogue electrical signal which is amplified by means of an amplifier 904 or a read-out circuit, for example a source follower. The signal from the amplifier 904 is detected by a sensor circuit 908 at a sampling frequency Fs (706). The sensor circuit 908 has an analogue/digital converter 910 which converts the signal from the amplifier 904 into digital signals. The sensor circuit also has a digital filter 912 which blocks high-frequency digital signals from the analogue/digital converter 910 (low-pass filter). The filtered digital signals are converted into a customer-specific 1-bit output signal 916 by a modulator 914 which is connected to the digital filter 912.
The low-pass filter is needed to stabilize the arrangement and to attenuate an excessive increase in the MEMS frequency response. A group delay is associated with this arrangement.
In some applications, for example headset applications, it is necessary to acoustically suppress the ambient noise by means of a loudspeaker which is driven in anti-phase. In this case, the interfering ambient noise is measured using a microphone, is then digitally processed and is switched to the loudspeaker. The group delay of the microphone arrangement plays a great role in the suppression. This group delay is additively composed of the group delays of the microphone, the group delay of the digital signal processing in the sensor circuit and the group delay of the loudspeaker.